This invention pertains to excimer lasers and, more particularly, to the conservation of the gases used in an excimer laser.
One of the most successful new laser technologies to have emerged in recent years is a new family of powerful gas lasers called excimer lasers. These lasers are unique in that they are efficient sources of high powered ultra-violet light. This property makes these lasers very useful for a wide range of scientific as well as industrial and military operations.
An economic limitation to the long-term use of excimer lasers has been the high cost of operation. A significant portion of this cost has been due to the consumption of expensive rare gases such as krypton or xenon as well as moderately expensive gases such as argon, helium and neon. Ordinarily, the lasing gas mixture which is a combination of a heavy rare gas, a diluent rare gas and a halogen gas is fed into the laser and withdrawn from the laser after the lasing has been performed. Because of the cost of the rare gases, the excimer laser can be expensive to operate. However, the present inventor was part of a team which developed a closed-cycle recirculating system for rare gas halide excimer lasers. The results of this invention were published in Applied Physics Letters, Volume 32 (5) on Mar. 1, 1978, starting on Page 291 thereof. (This idea is also discussed in Excimer Laser Chemical Problems, Los Alamos National Laboratory document Number Q-8-L-169..) While the proposed system has performed admirably to reduce the cost of the gases by virtue of the fact that the heavy rare gases are cleaned and recirculated after the removal of the halogen and fed back to the laser along with fresh halogen gas, there is a demand for better means for removing formed impurities.
In particular, it has been found that calcium metal, in the form of particles, is an excellent bulk getter of chemical impurities in rare gas streams. Furthermore, the efficiency of cleanup increases with temperature. However, because of the formation of calcium vapor at high temperatures, calcium particles tend to fuse together. This fusion can eventually form a plug which constricts gas flow through a tube containing heated calcium particles. To overcome the problem, large particles of calcium sponge have been used which somewhat extend the operating time before eventual plugging occurs.